This invention relates to evacuated tubular solar collectors and more particularly to a type wherein an outer tubular member surrounds an inner absorber member, and wherein the absorber member may move relative to the outer tubular member. The outer tubular member is closed to ambience and is evacuated while the absorber member is adapted to carry working fluid for the removal of sensible heat produced as a result of insolation. The improvement provides for a slidable coupling so that the outer tubular member may move relative to the absorber member upon expansion and contraction thereof under varying conditions of insolation, and for supporting the absorber member within the outer tubular member along a selected axis.
Evacuated tubular solar collectors of the type described herein utilize clips for centering and supporting an absorber within an outer tubular member. Such clips may take the form of extensions of the absorber surface which are of minimal surface area and which physically touch the outer tubular member. Stampings or springlike members may also be utilized to engage with the absorber and the inner wall of the outer tubular member to support one relative to the other and to allow for a certain amount of expansion of the absorber under insolation. It is also known to utilize insulating buttons or the like for supporting the absorber member within the outer tubular member.
Of the systems described above it is oftentimes difficult, expensive, and inefficient to provide optimal support. One reason for this is that the clips or springs are usually manufactured from metals which are highly conductive and produce thermal leaks from the absorber to the outer surface of the outer tubular member. Insulating buttons may be more desirable, however, they must be fixed about the circumference of the collector in the evacuated space more or less at even angular spacing. In any event they are sometimes difficult to insert in a manner adapted for rapid fabrication.
The present invention, on the other hand, utilizes a preformed outer tubular member having a sleevable portion and a preformed inner absorber member, which may be in the form of a member having a portion which engages with the preformed portion of the outer tubular member to form a sleevable or sleeved expansion joint. Means may be provided to cushion the inner and outer members one from the other, which means may be a spring-like member concentrically disposed in the sleeved expansion joint to support the absorber relative to the outer tubular member. The spring-like member is fabricated with minimal surface contact in the expansion joint for significantly reducing thermal leaks. The cushion means may be in the form of an insulator to further reduce thermal loss.
The present invention also provides for ease of fabrication since the outer tubular member and the absorber member are preformed, each carrying a portion of the expansion joint, and preassembled with the cushion means to reduce the final fabrication time.